I am building N/A 2789cc engine which has billet dual plug heads, fuel injected and CR 11:1 or 11.5:1, max rpm 7500. HP is about 250-270. ECU is finnish MS3 based ecu which has built in relays, all MS3X features and splashproof casing and 56 pin automotive connector.

What ignition coils to use? I was naturally thinking to use two wasted spark coils, like IGN-4 or VAG 032905106B

Vag coil has built in driver and it has proven at use with single use over 350hp.

I decided to go with a subaru coil pack from an early 2000's. the 4 wire ones are wasted spark with built in ignitors. and they use standard plug ends. got one for $10 at the local pick n pull with as much wire harness as I could cut off.
soon as I decide on a crank trigger I'll try it out.

The PROBLEM is when a "twin post" coil fires TWO sparkplugs in compression.

This coil was NOT designed to do this work.

The IGN-4A is FOUR single tower coils INSIDE one package.
The IGN-4A (Amplifier) has internal IGBT (4) used to drive the four coils.
Thus NO large drive current is required of the EMS for "twin channel" operation.

Depending on your project and what you are doing, Lance Pantera EFI could help you with the eight IGN coils. They are the best. I use four IGN1 coils direct fire. When I go dual plug I will get four more.

I still think 8 x IGN1A coils are not necessary on a N/A engine, which is not 100% race engine. And they cost 620€, waste of money. Two IGN4A coils should do the job perfectly, since i know even few OE wasted spark coils can support over 300hp on volvo B230 (stroked 2,7+) series N/A race engines.

I dont know how available GM v8's are where you are but I can get 8 Ls1 coils from a junk yard for a reasonable price. I've also seen full sets of used coils go for a decent price on ebay. they are often removed from stock motors to "upgrade" even though they are plenty powerful. if you get the stock ones with the little heat sinks on them they have built in ignitors.

Redline Weber did point out that the +/- output of a typical double ended twin tower coil was less than optimal if both are used to simultaneously fire the same cylinder, rather than one under compression in waste spark.

The following avoids the issue:
(You would need two 4 tower coil packs anyway for dual plug)

example: one wire per primary plug off one 4 output Subaru coil pack, and the second 4 wires the off the second coil pack to the secondary plugs, rather than using any pair of outputs from the same coils/cylinder.

That way no "pair" of +/- outputs from any single waste spark coil are trying to fire on compression at the same time.

I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

It may also allow firing the secondary plug before or after the primary on systems that support it.
(was being discussed for MS3+MS3x at least)

On some engines firing both "at the same time" may be optimal, but I'll wager it depends hugely on plug location and chamber shape.

I have always wanted to try a T4 wedged bathtub chamber with a 10mm plug at both ends of the trench.
To meet in the ~middle, he intake end plug would have to fire a few degrees earlier as the exhaust end flame speed would be higher due to the ex valve heat assist.

I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...